The present invention relates to a cold cathode field emission device and a process for the production thereof, and a cold cathode field emission display and a process for the production thereof.
In the field of displays for use in television receivers and information terminals, flat type (flat panel type) displays that can comply with demands for a decrease in thickness, a decrease in weight, a larger screen size and a higher definition are being studied as substitutes for conventional mainstream cathode ray tubes (CRT). Such flat type displays include a liquid crystal display (LCD), an electroluminescence display (ELD), a plasma display (PDP) and a cold cathode field emission display (FED). Of these, the liquid crystal display is widely used as a display for an information terminal. When attempts are made to apply it to a stationary television receiver, however, it still has problems to solve for attaining a higher brightness and a larger screen size. In contrast, the cold cathode field emission display uses cold cathode field emission devices (to be sometimes referred to as “field emission device” hereinafter) capable of emitting electrons from a solid to a vacuum on the basis of a quantum tunnel effect without relying on thermal excitation. The cold cathode field emission display is therefore attracting great attention in view of a high brightness and a low power consumption.
FIGS. 32 and 33 show one example of the cold cathode field emission display (to be sometimes referred to as “display” hereinafter) having field emission devices. FIG. 32 is a schematic partial end view of a conventional display, and FIG. 33 is a schematic partial exploded perspective view of a cathode panel CP and an anode panel AP.
Each field emission device shown in FIG. 32 is a field emission device that is a so-called Spindt-type field emission device having a conical electron emitting portion. The above field emission device comprises a cathode electrode 111 formed on a support member 110, an insulating layer 112 formed on the support member 110 and the cathode electrode 111, a gate electrode 113 formed on the insulating layer 112, an opening portion 114 made through the gate electrode 113 and the insulating layer 112 (first opening portion 114A made through the gate electrode 113 and a second opening portion 114B made through the insulating layer 112), and a conical electron emitting portion 115A formed on the cathode electrode 111 positioned in a bottom portion of the second opening portion 114B. Generally, the cathode electrode 111 and the gate electrode 113 are formed in the form of a stripe each and in directions in which projection images of these electrodes cross each other at right angles, and a plurality of field emission devices are generally formed in a region where the projection images of these electrodes overlap. Such a region corresponds to a region occupying one pixel and will be referred to as “overlap region” or “electron emitting region”. Further, such electron emitting regions are arranged in the effective field (field that works as an actual display portion) of the cathode panel CP such that they are arranged in the form of two-dimensional matrix.
The anode panel AP comprises a substrate 30, a phosphor layer 31 (31R, 31B, 31G) that is formed on the substrate 30 and has a predetermined pattern, and an anode electrode 33 formed thereon. One pixel is constituted of a group of the field emission devices formed in the overlap region of the cathode electrode 111 and the gate electrode 113 on the cathode panel side, and the phosphor layer 31 being on the anode panel side and facing the group of the field emission devices. In the effective field, such pixels are arranged, for example, on the order of several hundred thousand to several million. A black matrix 32 is formed on the substrate 30 that appears between such phosphor layers 31.
The anode panel AP and the cathode panel CP are arranged such that the electron emitting region and the phosphor layer 31 face each other, and bonded to each other in their circumferential portions through a frame 34, whereby the display can be produced. An ineffective field surrounding the effective field and having a peripheral circuit for selecting pixels (ineffective field of the cathode panel CP in the shown example) is provided with a through-hole 36 for vacuuming, and a tip tube 37 that is sealed after vacuuming is connected to the through-hole 36. That is, a space surrounded by the anode panel AP, the cathode panel CP and the frame 34 is vacuumed and constitutes a vacuum space.
A relatively negative voltage is applied to the cathode electrode 111 from a cathode-electrode control circuit 40, a relatively positive voltage is applied to the gate electrode 113 from a gate-electrode control circuit 41, and a positive voltage higher than the voltage applied to the gate electrode 113 is applied to the anode electrode 33 from an anode-electrode control circuit 42. When the above display is allowed to perform displaying, for example, a scanning signal is inputted to the cathode electrode 111 from the cathode-electrode control circuit 40, and a video signal is inputted to the gate electrode 113 from the gate-electrode control circuit 41. An electric field generated by the voltages applied to the cathode electrode 111 and the gate electrode 113 causes the electron emitting portion 115A to emit electrons on the basis of a quantum tunnel effect, and the electrons are attracted toward the anode electrode 33 to collide with the phosphor layer 31. As a result, the phosphor layer 31 is exited to emit light, and a desired image can be obtained. That is, the operation of the display is controlled, in principle, on the basis of the voltage applied to the gate electrode 113 and the voltage applied to the electron emitting portion 115A through the cathode electrode 111.
The method for producing a Spindt-type field emission device will be explained hereinafter with reference to FIGS. 34A and 34B and FIGS. 35A and 35B which are schematic partial end views of the support member 110, etc., constituting the cathode panel.
Basically, the above Spindt-type field emission device can be obtained by a method of forming each electron emitting portion 115A by vertical vapor deposition of a metal material. That is, deposition particles enter perpendicularly to the first opening portion 114A made through the gate electrode 113. However, the amount of deposition particles that reach a bottom portion of the second opening portion 114B is gradually decreased by the shield effect of an overhanging deposit that is formed in the vicinity of the opening edge of the first opening portion 114A, and the-electron emitting portion 115A that is a conical deposit is formed in a self-aligned manner. The method for producing the Spindt-type field emission device will be explained with regard to a method of forming a peel layer 116 on the gate electrode 113 and the insulating layer 112 beforehand for making it easy to remove an unnecessary overhanging deposit. FIGS. 34A and 34B and FIGS. 35A and 35B show one electron emitting portion.
[Step-10]
First, an electrically conductive material layer for a cathode electrode, for example, made of polysilicon, is formed on the support member 110 made, for example, of a glass substrate by a plasma CVD method, and then the electrically conductive material layer for a cathode electrode is patterned by lithography and a dry etching technique, to form the stripe-shaped cathode electrode 111. Then, the insulating layer 112 made of SiO2 is formed on the entire surface by a CVD method.
[Step-20]
Then, an electrically conductive material layer (for example, TiN layer) for a gate electrode is formed on the insulating layer 112 by a sputtering method, and then the electrically conductive material layer for a gate electrode is patterned by lithography and a dry etching technique, whereby the stripe-shaped gate electrode 113 can be obtained. The stripe-shaped cathode electrode 111 extends leftward and rightward on the paper surface of the drawing, and the stripe-shaped gate electrode 113 extends perpendicularly to the paper surface of the drawing.
[Step-30]
Then, a resist layer is formed again, and the first opening portion 114A is formed through the gate electrode 113 by etching, and further, the second opening portion 114B is formed through the insulating layer 112 by etching. The cathode electrode 111 is exposed in the bottom portion of the second opening portion 114B, and then, the resist layer is removed. In the above manner, a structure shown in FIG. 34A can be obtained.
[Step-40]
Then, while the support member 110 is turned, nickel (Ni) is obliquely deposited on the insulating layer 112 and the gate electrode 113, to form the peel layer 116 (see FIG. 34B). In this case, the incidence angle of deposition particles with respect to the normal of the support member 110 is determined to be sufficiently large (for example, incidence angle of 65 to 85 degrees), whereby the peel layer 116 can be formed on the gate electrode 113 and the insulating layer 112 almost without depositing nickel on the bottom portion of the second opening portion 114B. The peel layer 116 extends from the opening edge of the first opening portion 114A like the form of eaves, and due to the peel layer 116, the diameter of the first opening portion 114A is substantially decreased.
[Step-50]
Then, an electrically conductive material such as molybdenum (Mo) is vertically (incidence angle of 3 to 10 degrees) deposited on the entire surface. In this case, with the growth of an electrically conductive material layer 117 having an overhanging form on the peel layer 116 as shown in FIG. 35A, the substantial diameter of the first opening portion 114A is decreased, so that deposition particles that contributes to the formation of a deposit on the bottom portion of the second opening portion 114B come to be gradually limited to deposition particles that pass the center of the first opening portion 114A. As a result, a conical deposit is formed on the bottom portion of the second opening portion 114B, and the conical deposit constitutes the electron emitting portion 115A.
[Step-60]
Then, the peel layer 116 is removed from the surface of the gate electrode 113 and the insulating layer 112 by a lift-off method, to selectively remove the electrically conductive material layer 117 above the gate electrode 113 and the insulating layer 112. In this manner, a cathode panel CP having a plurality of Spindt-type field emission devices can be obtained.
For obtaining a large amount of current of emitted electrons at a low driving voltage in the above display, it is effective to acutely sharpen the top end portion of the electron emitting portion. From this viewpoint, the electron emitting portion 115A of the above Spindt-type field emission device can be said to have an excellent performance. The above process for producing the Spindt-type field emission device is an excellent process capable of forming a conical deposit, as the electron emitting portion 115A, in the opening portions 114A and 114B in a self-aligned manner. However, it requires a high processing technique to form such conical electron emitting portions 115A, and with an increase in size of the display and with an increase in area of the effective field, it is getting difficult to uniformly form such electron emitting portions 115A that are sometimes several tens of millions in number in the entire region of the effective field. Further, many apparatuses for producing semiconductor devices are used, and when the display is increased in size, it is required to increase the size of the apparatuses for producing semiconductor devices, which causes the display production cost to increase.
There has been therefore proposed a so-called flat-type field emission device that does not employ any conical electron emitting portion but employs a flat electron emitting portion exposed on the bottom portion of the opening portion. In the flat-type field emission device, each electron emitting portion is formed on the cathode electrode positioned in the bottom portion of the opening portion, and is constituted of a material having a lower work function than a material constituting the cathode electrode so that the electron emitting portion can accomplish a larger current of emitted electrons even if it has a flat form. In recent years, various carbon materials including carbon nanotubes have been proposed as the above material.
In the production of the above flat-type field emission device, for example, a negative-type photosensitive paste layer 118 containing carbon nanotubes is formed on the entire surface including the inside of the opening portion 114 after a structure shown in FIG. 34A is obtained (see FIG. 36A). Then, the photosensitive paste layer 118 is exposed to light (see FIG. 36B), followed by development and removal of the photosensitive paste layer 118 in an unnecessary region. Then, the remaining photosensitive paste layer 118 is fired, whereby the electron emitting portion 115 can be obtained (see FIG. 36C). A reference numeral 119 shows a mask for exposure.
When the photosensitive paste layer 118 is exposed to light, the mask for exposure 119 is positioned in regard to a reference marker (not shown) provided beforehand, for avoiding a positional deviation between the mask for exposure 119 and the opening portion 114.
However, the support member 110 suffers deformation, for example, due to the thermal history of the support member 110 or due to stresses, etc., of various layers (cathode electrode 111, insulating layer 112, gate electrode 113, etc.) formed on the support member 110. As a result, a positional deviation frequently takes place between the mask for exposure 119 and the opening portion 114 when the photosensitive paste layer 118 is exposed to light. When the above phenomenon takes place, the distance from the opening edge of the first opening portion 114A made through the gate electrode 113 to the electron emitting portion 115 positioned in the bottom portion of the second opening portion 114B varies, and as a result, the amount of emitted electrons varies among such electron emitting portions 115, which causes display non-uniformity to take place. In the worst case, the photosensitive paste layer 118 remains on the side wall of the opening portion 114 and forms a short circuit between the gate electrode 113 and the cathode electrode 111.